Method for the manufacture of hollow articles of thermoplastic material



Nov. 19, 1968 PIOTROWSKI 3,412,186

METHOD FOR THE NUFACTURE OP HOLLOW ARTICLES OF THERMOPLASTIC MATERIALFiled May 27, 1966 4 Sheets-Sheet 1 IN VEN TOR.

.... TADEUSZ PIOTROWSKI BY 22 Aha/ u.

ATTORNEYS Nov. 19, 1963 T. PIOTROWSKI 3,412,186

METHOD FOR THE MANUFACTURE OF HOLLOW ARTICLES OF THERMOPLASTIC MATERIAL4 Sheets-Sheet 2 Filed May 27, 1966 IN VlzjN TOR.

X I l Nov. 19, 1968 T. PIOTROWSKI 3,412,186

E OF HOLLOW ARTICLES OF THERMOPLASTIC MATERIAL METHOD FOR THE]MANUFACTOR 4 Sheet sSheet 5 Filed May 27. 1966 wow mow

INVENTOR.

TADEUSZ PIOTROWSKI ATTORNEYS Nov. 19, 1968 T. PIOTROWSKI 3,412,186

METHOD FOR THE MANUF OF HOLLOW ARTICLES OF THERMOP MATERIAL Filed May27, 1966 I 4 Sheets-Sheet FIGB FIG]

JNVENTOR. TADEUSZ PIOTROWSKI BY w ATTORNEYS United States Patent3,412,186 METHOD FOR THE MANUFACTURE OF HOLLOW ARTICLES OF THERMOPLASTICMATERIAL Tadeusz Piotrowski, Montreuil-sous-Bois, France, assignor toWorson S.A., Geneva, Switzerland, a corporation of SwitzerlandContinuation-in-part of application Ser. No. 225,604, Sept. 24, 1962,which is a continuation-in-part of application Ser. No. 765,662, Oct. 6,1958. This application May 27, 1966, Ser. No. 553,486 Claims priority,application France, Oct. 12, 1957, 749,319; July 1, 1958, 769,190 12Claims. (Cl. 26489) The present application is a continuation-in-part ofcopending application Ser. No. 225,604, filed Sept. 24, 1962, which is acontinuation-in-part of application Ser. No. 765,662, filed Oct. 6,1958, both abandoned.

The present invention relates to improvements in a method formanufacturing hollow articles of thermoplastic material from injectedblanks or preforms which are inflated or blown so as to take the shapeof the desired articles.

It is known in the prior art to effect such a process by pressing theedge of a substantially molten or pasty preform onto the neck of ahollow mold which has the shape of the desired articles. The preform isthen blown or inflated within this mold, starting from the edge thereof,until it completely touches against the walls of the mold and, oncontact with these walls, the distended preform cools instantaneously,thereby permanently assuming the shape of the mold, i.e., the desiredarticle.

For obvious reasons of production speed and in order to prevent thepasty preform from being left to its own weight between the injectionand blowing phases of the process, the blowing head is generallyincorporated in the core upon which the preform or parison is injected.

The core containing this blowing head is then conveyed to the entranceto the blowing mold.

For this latter reason, the compressed air channel for blowing, runsthrough'the core and terminates at the surface thereof by means of anoutwardly opening classic flap-valve. This valve may rise and allow theblowing air to escape. However, it also counters the penetration ofplastic from the exterior into the air channel, particularly performingthis function during injection.

However, in these presses, which are now Well known and currently on themarket, it is nevertheless impossible to manufacture, on a large scale,blown objects the walls of which are simultaneously:

Relatively thin, i.e., in particular, having a thickness of a few tenthsof a millimeter. This is very important with regard to the cost of thearticle which, on a mass production scale, is directly connected withthe amount of raw material used;

Of uniform thickness. With small thicknesses, all of the zones ofweakness in the article considerably affect the behavior thereof insubsequent mechanical operations, for example, capsuling when the blownobject is a receptacle. In addition, too great a thinness in aparticular area may lead to punctures in the preform;

Uniformly distended. The stretching of certain thermoplastic materials,such as polystyrene, leads to the orientation of the molecules thereof,thus producing exceptional mechanical characteristics therein. In thisway, if a fraction of the preform is transported but not distendedduring the blowing operation, a weak zone will be created in the blownobject;

Free from swelling or pleats. If swelling is localized initially incertain regions of the preform which are softer and exposed to the jetof blowing air to a great extent, extensions of the material areproduced which result in swellings and pleats in the wall of the blownlayer which fold back upon themselves upon reaching the wall of themold.

It is clear that any proportion, even very small, of defective articlesis a detriment to the manufacture there- .of on a mass production scale.For example, even a minute percentage of yogurt or milk containersbursting during capsuling, thereby soiling, splashing or covering thecapsuling machines with the product being processed, would be atremendous disadvantage and hindrance to the effective productionthereof.

However, the processes and apparatus used in the prior art for makingsuch articles create certain weaknesses therein which are barelydiscernible. This problem IS of particular importance since it isessential-in the course of such productions to blow uniformly a film ofextreme fineness and thinness which, therefore, is very fragile, therebymaking very unstable and uncertain the course of expansion thereofduring blowing.

The manufacture of such blown articles therefore requires an absoluteuniformity in the temperature of the preform at the time of blowing andin the mechanical expansion operation. These exigencies are practicallyimpossible to achieve in injection or blowing presses whose cores arefitted with the classical flap-valves, since the blowing air channel,the flap-valve, and the stern and return spring thereof occupy a largespace in the axis of the core. The result is that irrigation by a heatexchange fluid through the remainder of the core leads to suchstructural difliculties and such narrow assembly and tolerance limits inthe construction of the core and, finally, to an apparatus so fragileand hazardous in use that, for practical reasons, it has never beenpossible to combine a blowing valve and heat control by fluid irrigationin the same core with complete success. Yet, such irrigation by fluid isimperative when it is necessary to cool periodically and promptly toabout l80 C. a core on which the preform is injected at a temperature ofbetween approximately 180 and 240 C. In particular, certain polystyrenesinjected at between 200 and 220 C., must be cooled to about C. in orderto obtain an effective blowing thereof.

Moreover, serious diificulties arise when it is desired to blowmaterials having a low specific heat such as polystyrene, rather thanthe classical materials of large thickness, such as polyethylene. Thisis particularly true when it is desired to blow such materials having athickness of a few tenths of a millimeter, which is particularly thecase when the core has a shape and dimensions approaching those of thefinished article so that the regularity of the preform at the Wall ofthe finished article may be retained. Thus, during conveyance of thepreform from the injection chamber to the blowing mold, the pastythermoplastic film cools in a non-uniform manner under the influence ofthe ambient air and the core. For example, the temperature of the corecarrying the preform is higher in the region that is situated oppositethe injection orifices and which is subjected to the material coming outin hot form from the injection nozzle. The result is that thetemperature of the surface of the core which governs that of the film tobe blown must be promptly regulated so as to be uniform throughout.However, local irregularities and dissymmetry of temperatures of a fewdegrees are enough to cause ruptures, swelling and/or folds which areirreconcilable with mass production operations.

The same drawbacks are encountered when, instead of using athermoplastic material having a low specific heat, a material with ahigh specific heat is treated, such as polyethylene, and especially whena patsy layer of the preform is of small thickness.

The use of the classical flap-valves in the apparatus of the prior artalso does not allow for regular, uniform, progressive and yetinstantaneous expulsion of the blowing air. This is because theexpulsion is too concentrated locally when the valve is at the top ofthe core, whereby the diameter of the passage section is reduced. Inthis case, the flow of air does not permit a gradual raising of thepreform toward the walls of the mold and, thus, does not permit theplastic film to be laid gradually upon these walls.

When, on the contrary, the passage section of the valve is broughttoward the base of the core and the fluid circulation is provided insidethe latter, a valve is used whose fiap, which is formed by the entirecore, has an inertia which cannot be neglected. In addition, this flapis drawn toward its closed position by the return spring and theconnections of the hydraulic cooling system. It is therefore necessaryto put into operation appreciable blowing pressures in order to overcomethe return force and inertia, which pressures are a disadvantage inachieving the necessary uniform and turbulent-free expansion.

In addition, the latter-mentioned apparatus of the prior art haverelatively compact designs for the air expulsion means and for theentrance and exit of heat-regulating fluids. These factors, togetherwith the relative distention of the various elements of the core, renderthe guidance of the flap particularly precarious and delicate and,consequently, render the positioning of the core particularly difficult.The result is that the core is sometimes moved laterally under thepressure of the plastic during injection, causing an irregulardistribution of the preform on the core to be produced.

It has also been proposed in the prior art to replace the mobileflap-valves which rise under the pressure of the blowing gas withpermanent orifices which are small enough to prevent penetration by theinjected plastic material into the blowing air channel while allowingthe air to escape at the same time. However, it has not been possible toachieve this proposal in practice since the only types of orifices whichhave been produced are in the form of pores and, in particular, in coresof porous cast iron. Injected plastic infiltrates and becomes implantedin these pores during the injection step, so that during blowing thepreform adheres to the core at numerous points on its surface, wherebyexpansion thereof cannot take place correctly. In addition, porous castiron, by its very nature, cannot be used with an internal irrigationsystem which, as stated above, is absolutely necessary in order toobtain an instantaneous heat regulation.

Thus, cores for blowing thin preforms having a heat regulation by meansof fluid circulation as well as open or classical valve-type orificeshave not produced satisfactory results on a practical level.

Therefore, one of the objects of the present invention is to provide aprocess which is carried out within an injection blowing machine andwhich involves a uniform heat control of the thermoplastic blank by ageneralized and homogeneous irrigation of the surface of the core, andthe uniform temperature of the core and the blank being maintainedduring transfer of the same from the injection to the blow mold.Moreover, the blowing orifice arrangement of the present invention doesnot affect this type of heat control.

The blowing orifice arrangement in accordance with the present inventionhas also proved to be particularly effective in blowing pre-injected,cooled and stored preforms which are subsequently reheated on a corebefore being blown therefrom. It is, in fact, very difiicult to reheatsuch cold preforms by placing them in close contact onto aheated corebecause the pre-injected preforms which are produced at high speedbecome distorted during cooling and because it is practically impossibleto place them correctly without local deformation or sagging on a veryhot core. Thus, articles obtained by the blowing of such preforms areusually not satisfactory.

Thus, another object of the present invention is to provide a blowingorifice arrangement which may be enlployed in the blowing of previouslystored preforms.

In addition, it has been observed that the bringing of injected orapplied preforms quickly and at an absolutely even temperature onto acore subjects the semi-fluid preform to superficial or thermal internaltension forces which result in a leakage toward the base of the core ofthe material which is at the point or top of the core. This phenomenonis particularly noticeable where materials are used which do not adherewell to the core, such as polystyrenes having an appreciable content ofrubber, for example, copolymerized with butadiene, or when the injectedmaterial is not yet sufliciently softened. In such a case, the verythin, pasty material coating the core and held by its base tends tocontract. When this contraction is not very rapid, the central part ofthe base of the article may diminish to a very thin veil or it may evenburst.

Therefore, another object of the present invention is to provide meansfor preventing such weaknesses and ruptures in blown articles.

Still another object of the present invention is to reduce the transferbetween the injection and blowing means to a series of very briefmovements and to render the size of these means as a whole and of thecore small enough so that the entire means may be mounted on classicalcolumn-type injection presses.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art from a consideration of thefollowing specification and claims and of the attached drawings wherein:

FIGURE 1 shows a longitudinal cross-section of the preform core inaccordance with the present invention within a blowing chamber;

FIGURE 2 is a transverse section taken along the line 2-2 of FIGURE 1FIGURE 3 is an enlarged sectional view of the slot at the base of thecore;

FIGURES 4A and 4B show a longitudinal cross-section of the structure ofthe core in accordance with the present invention, FIGURE 4A showingsaid core within an injection chamber and FIGURE 4B showing said corewithin a blowing mold;

FIGURES 5A and 5B are transverse sections taken along the line 55 ofFIGURES 4A and 4B, respectively;

FIGURE 6 is a side elevation of a blowing and injection apparatus inaccordance with the present invention;

FIGURE 7 is a transverse section taken along the line 77 of FIGURE 6;

FIGURE 8 is a transverse section taken along the line 8-8 of FIGURE 6;

.FIGURE 9 is a transverse section taken along the line 9-9 of FIGURE 6;and

FIGURE 10 is an enlarged view of a core in accordance with the presentinvention within the apparatus of FIGURE 6.

FIGURE 1 shows a core in accordance with the present invention within ablowing mold. A hood 23 is screwed at the lower neck portion thereof 24onto a threaded shoulder 25 provided at the base of a shaft 26. At itsmost downward position, hood 23 rests on face 27, while its lower edge28 remains at a certain predetermined distance, referred to in detailbelow, from an underslung annular crown 29 circumscribing the bearingcrown 27.

A toric channel 30 forms a decompression chamber or an annular collectorwhich feeds the slot 31 which remains open at the base of the hood 23.Channel 30 is fed by a channel 38 running through collar 33 of the shaft26.

The oil used for regulating the temperature is admitted through oilintake or supply pipe 35, having channels 22 which prevent the backflowof oil. The oil spreads out in a uniform manner therefrom from the topof the shaft 26 toward the base thereof under hood 23. The oil isremoved by means of radial piping 36.

The transverse section view in FIGURE 2 shows more clearly the conduitsa and grooves b which are used for removing the oil from the core.

Returning to FIGURE 1, an annular ring 39, preferably isolated from theremainder of the core by mica or grooves whereby a throat 40 between thesame and crown 29, is traversed by circulating cooling water in anannular pipe 41. This water enters at 42 and returns at 43.

To achieve perfectly distinct oil and blowing air circuits, a joint, notshown, may be provided between the region of the inner edge of the hood23 and the shaft 26 or the annular face 27.

Thus, the core block shown in FIGURE 1 essentially comprises:

(1) A face plate whose temperature is perfectly controlled, since theoil circulates just under the surface of hood 23. In addition, thesummit or top of the hood, being highly heated since it repeatedlyreceives, during the injection step, the injected plastic before it hasbegun to cool, is directly exposed to the oil admitted through piping35.

(2) A throat 40 situated at the base of the hood 23 and so cooled thatthe edge of the preform, injected into this throat to form the neck ofthe blown article or receptacle, is firmly held in place outside theinjection chamber during the disengagement of the preform and during itsconveyance to the blowing mold.

(3) A collar 33 which insures the interchangeable positioning of thecore and (4) A slot 31 situated at the base of hood 23, being veryclosely positioned with respect to what becomes the neck of the blownobject.

It is this slot 31 which distributes the blowing air evenly all aroundthe core and regulates the flow thereof since it forms a throttling ofsmall cross-section at the end of the feed piping. In this way, the sameconditions of expulsion of blowing air, whatever the small variations inblowing pressure may be, are assured of being reproduced. Similarly,when the blowing air feed pipes simultaneously feed a series of cores,there need be no fear of a sudden decompression in the apparatus if oneof the preforms bursts during its expansion.

Moreover, since slot 31 is permanently open, the air in channel 30 mayescape freely and will not hinder the penetration of the injectedplastic. In fact, this air may even be suctioned over the hood 23 bymeans of slot 31.

When the injected preform is blown on hood 23 and the preform has takenthe shape shown at 44 in the two blowing half-mold shells 45 and 46, ahyperpressure remains on the inside of the mold. Since slot 31 remainsopen in spite of this hyperpressure, it is very easy to release it byputting the piping 38 in communication with the atmosphere. Thus, as aresult, the core block may be removed from the blown object without thisinternal hyperpressure producing a fissure or rupture of the edge of thearticle as a result of vibrations set up by a sudden escape of airaround the edge of the article within throat 40.

Therefore, it can be readily seen from FIGURE 1 that the classical valveemployed in the prior art has been replaced in accordance with thepresent invention by a so-called static valve, i.e., one containing nomoving parts.

FIGURE 3 shows an enlarged view of said slot 31 together with itsclosely associated structure. The reference numerals thereon are thesame as described in FIG- URE 1.

During injection, the thermoplastic material must be prevented fromentering slot 31. It has been determined that this can be achieved ifthis.slot, or more generally, the orifice or orifices of blowing, has awidth or gap lower than a certain critical value, called the criticalpenetration threshold of the plastic material.

It is obvious that this threshold value, as well as the number oforifices, is related to the injection pressure, the viscosity of thethermoplastic material, the Volume of the object to be blown and thetemperature of the thermoplastic material at the time that it reachesthe orifice during injection. In particular, where the thermoplasticreaching the orifice is but slightly fluid, for example, when apolyethylene preform is injected onto a relatively cold core, the limitof the critical penetration threshold value can be appreciably increasedup to the tolerances usually allowed for the molding of joint planes.

In practice, it has been determined that when polystyrene is injected ata temperature of about C. and under a pressure of 7,110 lbs. per sq.inch (500 kg./cm. the threshold value is about 25 microns.

It may be observed from FIGURE 1 that the bottom of the blowing mold ispartially constituted by the rounded surface of a cylindrical piston 47housed between the two half-mold shells 45 and 46 which is adapted toslide by means of its stem 48, which latter moves in a plate 49.

When the hood 23, covered with the thermoplastic preform, is introducedinto the blowing mold, as shown in FIGURE 1, and when, because of therate of output, the softened condition of the plastic is not perfect, itis seen that the semi-fluid summit of the preform tends to move in thedirection of arrow f However, since the preform is already extremelythin, it is retained by the cooled base of annular ring 39.Consequently, the superficial internal or thermal tensions tend to bringabout localized thinning of the preform and to burst the preform in theregion of its summit at the top of the core. This is why, on the onehand, steps are taken during injection to insure that on leaving theinjection mold the preform has a certain thickness 50 (FIGURE 4A) in theregion of its summit and, on the other hand, the head of the piston 47is applied to the summit or top of the preform as soon as it is situatedin the blowing mold sections 45 and 46. As a result of this lattercontact, the preform cools instantaneously in situ, and a localhardening occurs in this region. When this happens there is no longerany fear of the preform bursting, and the piston 47 may be raised againand the lower surface thereof restores the continuity of the wall of theblowing chamber. When air is expelled by the slot 31, the excessthickness 50, more or less crushed by the piston, becomes an inherentpart of the remainder of the expanded preform.

A trademark may be engraved on the piston 47, and it will not bedeformed during the expansion of the preform, thus allowing a readilyidentifiable mark to be placed on the molded article or receptacle.Also, the use of certain marks in different blowing molds permitsimmediately the identification of a defective mold in the event of theproduction of defective articles.

The risks of puncture of the thermoplastic material at the top or summitof the preform may also be considerably reduced by having theplastification of the material be as complete and as homogeneous aspossible. Thus, when the plastic consists of a mixture of particleswhich varies from the fluid to the barely pasty state, considerabledifficulties are encountered. This is why it is preferred that, beforeinjection, internal heat exchange within the mass of pasty thermoplasticmaterial to be injected has been stabilized so as not to affect the rateof production of the desired articles. Hence, conventional injectionchambers wherein the thermoplastic material is heated in the region ofthe walls are to be avoided, while either screwtype presses or presseswhere the trajectory and the speed of the thermoplastic material betweenthe beginning of heating and the injection chamber enable any heatexchange to become stabilized and uniform may be readily employed in thepresent invention.

FIGURES 4A and 4B illustrate a cross-sectional view of a modification ofthe core shown in FIGURE 1. FIG- URE 4A shows the core in an injectionchamber, while FIGURE 4B shows the core in a blowing mold.

In this modification, piston 47 shown in FIGURE 1 is unnecessary becausehood 23a bearing the preform itself crushes the summit of the preformagainst the bottom of the blowing mold 52. Thus, an engraving maytherefore be made both on the bottom 52 of the blowing mold and on thesummit 53 of the hood 2311.

It should also be observed that hood 23a is mounted in a differentmanner :from that of hood 23 shown in FIG- URE 1. In particular, hood23a slides by means of longitudinal grooves 55 on shaft 26a.

The transverse view at line 5 of FIGURES 4A and 4B shown in FIGURES 5Aand 5B shows more clearly these latter mentioned guiding means for thehood, which are essentially constituted by the cylindrical wall of thecore at the level of the grooves 55. Aside from the function of thecirculating oil in regulating the temperature of the core, it alsoserves to partly lubricate the sliding or gliding between the core andthe shaft.

The extent of this sliding is very small and is limited by three gudgeonpins 56 screwed into the bottom of hood 23a, the heads 57 of which abutseatings provided on the back face of collar 33a of shaft 26a. Gudgeon56, which limits the width of the slot, is shown in FIGURE 4A in a lowposition, i.e., with the slot closed. The slot 31a in FIGURE 4B is shownin the open position.

In order to avoid unnecessary repetition, similar elements in FIGURES 1and 4A and 4B have the same numbers and are merely differentiated by theuse of a. Thus, in FIGURES 4A and 4B, ducts 35a, 38a and 41a areanalogous to the temperature regulatory fluid, the air and the coolingwater ducts shown as 35, 38 and 41, respectively, on FIGURE 1.

Hood 23a slides on a smooth bearing provided at the base of shaft 26a,and a joint 59 insures substantially complete air-tightness between duct36a and slot 31a, which slot is opened when the hood is freely dawntoward the top of the structure by a spring 60. As can be seen fromFIGURES 4A and 4B, spring 60 is situated at the upper part of the shaft26a. The circulation of a temperature regulating fluid such as oil inthe vicinity of this spring is maintained.

It will be observed that the core in FIGURES 4A and 4B contains a slot31a which does not have a fixed opening as in the case of slot 31 shownin FIGURE 1. However, slot 31a is permanently opened by spring 60,except when axial pressure F of great intensity is applied to the hood23a.

The latter embodiment of the present invention has certain distinctadvantages in certain cases and when, for reasons of production rate orbecause of some particular operation of the apparatus, it may benecessary to increase the injection temperature or to use a more fluidmaterial or to increase the blowing temperature. These characteristicshave an influence on the critical penetration threshold, and it mayhappen that a slot having a fixed gap distance, as shown in FIGURE 1,under certain of these conditions may be too large. Thus, thethermoplastic material would infiltrate the slot, cool within it andthereby obstruct it more or less, in spite of the blowing air whichtends to unblock the slot thereof. This results in an uneven anddissymmetrical distribution of the blowing air and, consequently, anuneven expansion of the preform, zones of weakness and even blisters,punctures or folds in the objects obtained. These results could only betaken care of in the past by dismantling the core and cleaning the slotwhich, of course, is time-consuming and expensive.

However, in accordance with the embodiment shown in FIGURES 4A and 4B,the slot 31a is normally retained opened by the powerful spring 60exerting a permanent counterpressure. However, when the pastythermoplastic material injected under high pressure at 63 penetratesinto the injection chamber, the spring is compressed under an enormouspressure F and the slot 31a closes, thereby preventing any infiltrationof thermoplastic material into the blowing slot.

Since, on the one hand, the pressure of the thermoplastic materialincreases evenly between the beginning and the end of injection andsince, on the other hand, the relationship governing this increase is ina very complicated relationship with respect to the characteristics ofthe cooling network, the specific heat of the material, the shape of thepreform, etc., it is very difficult to indicate at what precise momentthe slot will close or, even, whether it will close. The essential pointis that at the time the plastic material reaches the slot, the spring issufficiently compressed so that the opening of the slot 31a is less orequal to the crital threshold for which the particular thermoplasticmaterial, considering its pressure and its viscosity, would tend topenetrate therein.

It is therefore sufficient that, when the slot 31a is completely open,its gapas a safety measureshould correspond to the maximum criticalthreshold determined under the most unfavorable conditions ofpenetration, and that the spring 60 should give way under the injectionpressure thereof.

Spring 60 should also be able to resist the closing of the slot when thethermoplastic material at 51 is crushed between the bottom 52 of themold and the extremity 53 of the core, at the time when the latter isinserted into the blowing mold.

In certain circumstances, spring 60 may be situated at the base of theassembly although this variation is not as satisfactory as theembodiment shown in FIGURES 4A and 4B because of the possibility of thehood being moved or pushed laterally, thereby giving rise todissymmetric expansion of the preform. Thus, an arrangement wherein aslot having a fixed gap distance, as in FIG- URE 1, or wherein movableparts which have but very little play and exert considerable tension, asshown in FIGURES 4A and 4B, is preferred in order to allow permanentcentering of the core and complete irrigation of its mass at one and thesame time.

The cores illustrated herein are in the shape of long mandrels, but itis possible to use very short or even very flat mandrels, the shapethereof limited only with respect to the desired shape of the blownobjects. The static valve, i.e., the slots having a fixed width or gap,could, in this case, be provided in the form of one or several slotsbetween the opposite cylindrical surfaces of concentric crowns.

Finally, it should be noted that the slot 31a and the edge 68 (FIGURE4B) of the blowing mold are so positioned that the plastic film tends tolie exactly in the direction of the blowing gas, thereby conferring uponthe neck of the finished article a shape including a angle. In this way,the neck of the finished article has exceptional rigidity, and thereneed be no fear that it will break away from its stopper aftercapsuling. Similarly, this edge 68 makes it possible to retain the blownthermoplastic material 44a firmly during disengagement of the core block33a. In particular, in the case of yogurt containers, there is no dangerthat the neck of the containers, more or less squeezed among the variouspackages in a shopping basket, will become opened within the basket. Theaffixing of capsules or tops on the injected and perfectly shaped neckmay also be improved by corrugation or by small stops provided under theneck. Thus, in accordance with the present invention, cores havingblowing orifices which are normally open and through which the air maypass in both directions, which is not the case with cores where theorifices are fitted with classical flap-valves, has allowed theelimination of the difiiculties heretofore encountered in blowingpre-injected cooled and stored preforms which are reheated on a corebefore being blown therefrom.

FIGURE 6 illustrates an apparatus for manufacturing articles ofthermoplastic material by expansion molding utilizing the preform coresof the present invention. At the right of FIGURE 6 is a screw-typefeeding machine which feeds plastic material into nozzle 5. This machineconstitutes endless screw v with its motor drive M as well as theplastification or softening chamber C and thermoplastic powder feedgullet G.

Jacks 90 and 91 operate block 78 which supports the preform cores. Block78 glides on columns 73 and 74. Elements 76 and 77 represent theinjection chambers,

while elements 86 and 87 are the blowing molds. Block 85, which supportsthe blowing molds, is driven by knuckle joints 108 and 109. The knucklejoints are driven by means of jack 200 whose piston axis 201 is providedWith teeth 202. These teeth 202 cooperate with teeth 203 of a sector 204which pivots around an axis 205, the latter being integral with theframe.

A rod 206 is connected, on the one hand, to sector 204 by means of axle207 and, on the other hand, to the knuckle joints 108-109 by means ofaxle 208. Another rod 209 is connected, on the one hand, to the frame bymeans of axle 210 and, on the other hand, to the end of the knucklejoints by means of axle 208.

When jack 200 acts in the direction of the arrow Fa, the sector pivotsin the direction F b. The axle 207 is then displaced downwardly andforces the rod 209 to be placed in the position next to the horizontalin conjunction with the intermediary action of rod 206. Under thiscondition, the knuckle joint 108 forces the block 85 to be displacedtoward the right of the apparatus shown in FIG- URE 6 at the moment ofthe blowing phase of the process.

In the central block 78, which is adapted to pivot by means of motor 103together with the intermediary action of pinions 99 and 100, there aredisposed the inlet pipes for the temperature regulating fluid, forexample, oil, at 104 and for the cooling water at 106.

FIGURE 7 is a transverse sectional view showing the device used forclosing the molds. This means constitutes the two jacks 118 and 119. Thejack 118 is integral, on the one hand, with the half-mold 117 and, onthe other hand, with the half-mold 115. The two half-molds 115 and 117are connected by means of connecting rods 211 and 212. The jack 119 isconnected, on the one hand, to the half-mold 114 and, on the other hand,to the half-mold 116. These two half-molds 114 and 116 are connected toeach other by means of connecting rods 213 and 214. When the molds areclosed, the half-molds 115 and 117 are displaced as a single blocktoward the right, while the half-molds 114 and 116 are displaced as asingle block toward the left.

Element 112 designates the supply inlet of the fluid used for theblowing operation. Columns 73 and 74 are the support columns for themachine.

FIGURE 8 illustrates a transverse sectional view of FIGURE 6 taken atthe line 88. The central block 78 contains four cores, 81, 82, 83 and84. Pinion 99 is geared with pinion 100 mounted on shaft 101, therotation of which is effected by jack 103. The inlet pipes for, forexample, the circulating oil and the cooling water, are shown aselements 104 and 106, respectively. The uniform supply of compressed airfor the blowing step is effected by means of orifice 113.

FIGURE 9 illustrates a sectional view of the preforming molds (injectionchambers), such as 76 and 77. Jacks 90 and 91 operate the block 78 whichsupports the cores which are inserted thereinto.

FIGURE 10 is an enlargement of one of the cores 81 contained in theapparatus of FIGURE 6, this core being constructed in accordance withthe present invention, such as illustrated in FIGURES 1 and 4A and 4B.

It should be clear from a consideration of the drawings that when a filmof injected thermoplastic material is disposed on the cores, forexample, 81 and 82, the cores 181 and 182 come to cooperate with molds186 and 187. The jack 103 is then actuated to control the rotation ofthe element 78, and the knuckle joints 108 and 109 cause element 85 toslide, which actuates the element 78 to move to the right such thatcores 181-184 become positioned within molds 186487 and 86-87,respectively. During this movement, the passageway 112 adapts itself tothe orifice 113 to permit the delivery of air to the cores for theblowing step. At the same time, cores such as 81-82 have been positionedwithin the injection chambers such as elements 76 and 77. Thus, theinjection orifices become posizioned properly with respect to theinjection nozzles.

The machine is then ready for a new injection on the cores such as 81and 82 and a new expansion from the preform blanks disposed on coressuch as 181 and 182. The temperature of the thermoplastic blanks is thenstabilized in accordance with the present invention. Then, the knucklejoints 108 and 109 are employed to withdraw element 85 until it isreturned to the position shown in FIGURE 6. Jacks 118 and 119 controlthe opening of the molds such as 86 and 87 to permit the removal of theexpanded articles. Jacks 90 and 91 control the movement of block 78.

I claim:

1. A method of forming hollow articles of thermoplastic materialcomprising the steps of injecting said thermoplastic material onto atleast one preform core contained in an injection chamber, simultaneouslyblowing a thermoplastic preform contained on at least one second preformcore in a blowing mold by means of a fluid under pressure, the base ofsaid second preform core being disposed opposed to the base of saidfirst preform core, the bases of both cores being disposed on a commonplate, simultaneously withdrawing, by translational motion, theinjection mold and the blow mold containing the finished article fromthe first and second preform cores, said blow mold also simultaneouslyseparating to permit the finished article to fall from the mold,rotating the plate containing said preform cores about an axis normal tothe translational motion and inserting, by translational motion, saidfirst core into the blowing mold and said second core into the injectionmold.

2. The method of claim 1, wherein said steps are repeated in sequence soas to obtain a continuous production of said hollow articles.

3. The method of claim 1, wherein said plate is rotated through 4. Themethod of claim 1, wherein during blowing of said thermoplastic preform,said fluid under pressure is admitted to said core through an annularslot at the bottom of said core, and wherein during the injecting ofsaid thermoplastic material onto said preform core, a vacuum is pulledthrough said slot.

5. A method of forming hollow articles of thermoplastic materialcomprising the steps of injecting said thermoplastic material onto atleast one preform core contained in an injection chamber, simultaneouslyblowing a thermoplastic preform contained on at least one second preformcore in a blowing mold by means of a fluid under pressure, said corehaving a temperature suitable for blowing by circulating a heat exchangefluid uniformly beneath the surface of said core, the base of saidsecond preform core being disposed opposed to the base of said firstpreform core, the bases of both cores being disposed on a common plate,simultaneously withdrawing by translational motion the injection moldand the blowing mold containing the finished article from the first andsecond preform cores, said blowing mold also simultaneously separatingto permit the finished article to fall from the mold, rotating the platecontaining said preform cores about an axis normal to the translationalmotion and inserting, by translational motion, said first core into theblowing mold and said second core into the injection mold, thetemperature of the core being controlled during said rotating andinserting steps by circulating the heat exchange fluid uniformly beneaththe surface of the core.

6. The method of claim 5, wherein said steps are repeated in sequence soas to obtain a continuous production of said hollow articles.

7. The method of claim 6, wherein said plate is rotated through 180.

8. The method of claim 5, wherein the preform core is placed andmaintained in a predetermined relationship with respect to the walls ofthe injection chamber.

9. The method of claim 5, wherein during blowing of said thermoplasticpreform, said fluid under pressure is admitted to said core through anannular slot at the bottom of said core, and wherein during theinjecting of said thermoplastic material onto said preform core, avacuum is pulled through said slot.

10. The method of claim 5, wherein the fluid under pressure isintroduced into the blow mold against the lip of the article beingformed.

11. The method of claim 5, wherein said thermoplastic preform is broughtinto contact with a cold piece positioned within said blowing moldopposite the top point of said preform before said top point of saidpreform bursts.

12. The method of claim 5, wherein a uniform temperature is maintainedduring transfer of the core from the injection phase to the blow ;moldby circulating a heat exchange fluid uniformly beneath the surface ofsaid core. 20

References Cited UNITED STATES PATENTS 9/1954 Swartz 1845 5/1957Hardgrove 185 7/1944 Hofman 185 9/ 1958 Gussoni 18-5 12/1964 Cheney26497 5/1960 Sherman 26497 10/1943 Kopitke 26497 FOREIGN PATENTS 12/l953Australia.

3/1959 France.

ROBERT F. WHITE, Primaiy Examiner.

A. R. NOE, Assistant Examiner.

1. A METHOD OF FORMING HOLLOW ARTICLES OF THERMOPLASTIC MATERIALCOMPRISING THE STEPS OF INJECTING SAID THERMOPLASTIC MATERIAL ONTO ATLEAST ONE PREFORM CORE CONTAINED IN AN INJECTION CHAMBER, SIMULTANEOUSLYBLOWING A THERMOPLASTIC PREFORM CONTAINED ON AT LEAST ONE SECOND PREFORMCORE IN A BLOWING MOLD BY MEANS OF A FLUID UNDER PRESSURE, THE BASE OFSAID SECOND PREFORM CORE BEING DISPOSED OPPOSED TO THE BASE OF SAIDFIRST PREFORM CORE, THE BASES OF BOTH CORES BEING DISPOSED ON A COMMONPLATE, SIMULTANEOUSLY WITHDRAWING, BY TRANSLATIONAL MOTION, THEINJECTION MOLD AND THE BLOW MOLD CONTAINING THE FINISHED ARTICLE FROMTHE FIRST AND SECOND PREFORM CORES, SAID BLOW MOLD ALSO SIMULTANEOUSLYSEPARATING TO PERMIT THE FINISHED ARTICLE TO FALL FROM THE MOLD,ROTATING THE PLATE CONTAINING SAID PREFORM CORES ABOUT AN AXIS NORMAL TOTHE TRANSLATIONAL MOTION AND INSERTING, BY TRANSLATIONAL MOTION, SAIDFIRST CORE INTO THE BLOWING MOLD AND SAID SECOND CORE INTO THE INJECTIONMOLD.